Roberto Castro pitched in after hitting his approach shot into the water to save par at the 18th and complete a 71 to join the party at seven-under-par 206 along with Andres Romero of Argentina, and Americans Bill Haas and James Driscoll.
One stroke back was long-hitting Jason Kokrak, who powered a 349-yard drive at 18 on his way to finishing a 70 for 207, one stroke better than Tom Gillis and South Korea's Charlie Wi.
Wi made nine birdies, including seven on the front nine, on his way to a 65.
Jordan Spieth, a 19-year-old who began the round sharing the lead with Castro, held an early two-stroke lead after opening the third round with a pair of birdies to reach nine under par, slipped back to four under, three strokes off the pace.
Romero, who had to finish five holes early Saturday morning to complete the weather-interrupted second round, made four early birdies in the third round to reach 10 under par and seize a three-stroke lead.
But the Argentine double-bogeyed the 11th and bogeyed the 12th to set up the log jam at the top.
Haas triple-bogeyed the 11th after dumping a wedge shot into the pond right of the green as player fortunes rose and fell throughout the round as they aimed at pins often placed on the edge of trouble.
Because of a threat of stormy weather forecast for late Sunday afternoon, players will again go off both tees in groups of three beginning at 8:30 a.m. ET (1230 GMT) with the final groups teeing off two hours later.
(Reporting by Larry Fine in New York,; Editing by Gene Cherry)